i have s5 100u system consists of one Ai  (4-20 mA), one Ao (4-20mA) one DI and one DO for controlling melt pump

Please Help me in understanding the code in the attachment.

Hello,

at the attachment you can see your commented document 

Please look also at this limks:

https://support.industry.siemens.com/cs/document/16622054/simatic-s5-documentation-on-cd-rom-in-german-and-english?dti=0&lc=en-WW

and also

https://support.industry.siemens.com/cs/document/1091978/s5-100u-programmable-controller?dti=0&dl=en&lc=de-WW

At the second link can you se in the manual the commands and also a description of analog values (chapter 11)

I hope this help you for understanding the code of your FB

regards
CaOd